Calibrating pressure switches at extra low-pressure setting

ABSTRACT

The force or degree of compression of the spring is adjusted by rocking the lever about its axis A-B by means of the manually operated cam acting on the lever at D. Calibration for the lowto-high range is effected by adjusting the screw at B to rock the lever about axis A-D. For &#39;&#39;&#39;&#39;extra low&#39;&#39;&#39;&#39; settings, the cam is turned so the tab at D can, in effect be unlimited on its rise and the calibration is then effected by adjusting the limit screw acting on tab E. Any tool forces applied to either adjusting screw during calibration cannot be transmitted to the spring to adversely effect calibration.

i United States Patent Erich Kothe Schiller Park, lll.

Dec. 22, 1969 Aug. 17, 1971 Controls Company of America Melrose Park, Ill.

Inventor Appl. No. Filed Patented Assignee CALIBRATING PRESSURE SWITCHES AT EXTRA UNlTED STATES PATENTS 3 1940 Hastings 3,283,099 11/1966 Liebermannetal 337/318 3,325,614 6/1967 Rhodes ZOO/83 WM 3,359,387 12/1967 Rhodes ZOO/83 WM ABSTRACT: The force or degree of compression of the spring is adjusted by rocking the lever about its axis A-B by means of the manually operated cam acting on the lever at D. Calibration for the low-to-high range is effected by adjusting the screw at B to rock the lever about axis AD; For extra low" settings, the cam is turned so the tab at D can, in effect be unlimited on its rise and the calibration is then effected by adjusting the limit screw acting on tab E. Any tool forces applied to either adjusting screw during calibration cannot be transmitted to the spring to adversely effect calibration.

CALIBRATING PRESSURE SWITCHES AT EXTRA LOW- PRESSURE SETTING CROSS-REFERENCES TO RELATED APPLICATIONS The lever or wobble plate mechanism for achieving accurate calibration is claimed in patent application, Ser. No. 881,207, filed Dec. 1, 1969. 1

Pressure switches providing for extra low settings are shown in patent application; Ser. No. 887,898, filed Dec. 24, 19.69.

BACKGROUND OF INVENTION to-high calibration is not adequate to achieve the desired accuracy for the extra low setting.

SUMMARY OF INVENTION The present construction'provides a lever which can be adjusted about an axis defined by a fixed pivot point A and a pivot point B which is also a calibrating screw. The lever is in the general form of a plate with the adjusting cam acting at a point D remote from the calibrating axis. The lever acts on the spring at'a fourth point C remote from the other points. When the calibrating screw at B is moved, the lever rocks about axis A-D and moves point C to calibrate the spring-Tool forces applied to the screw during calibration cannot influence the spring. This construction is shown. and claimed in patent application, Ser. No. 88l,207, filed Dec. 1, 1969. The calibration achieved at B is not satisfactory for also achieving proper calibration at extra low settings of the pressure switch.-Therefore, the adjusting cam is shaped to, in effect, remove the cam as a factor at extra low settings and limit the rise of the plunger under influence of the pressure switch spring system by having the lever rise until tab E hits the calibrating screw. This permits very close calibration for extra low settings.

DESCRlPTlON or DRAWINGS I shows some additional features.

FIG. 3 is a side elevation of the pressure switch of FIG. 2. FIG. 4 is a perspective view of the adjusting cam per se and showing the tab or point D in relation to the cam surface.

DESCRIPTION OF PREFERRED EMBODIMENT The details of the pressure switch are not shown here. It is only important to know that the compression of the spring is to be adjusted in use and the unit should be calibrated at the factory so the actual force of the spring corresponds to the indications associated with the manual adjusting arrangement. The spring 10 is housed in a plunger 12 which lies under one comer C of the generally rectangular lever 14. The lever is pivoted at A in the fixed bracket 16 while another corner B is provided with a finger 18 which is formed and notched at 20 to fit over and beguided by the adjacent bracket portion 22 which carries the calibrating screw 24 against which the finger l8 bears by reason of the bias of spring 10.-This point can be called B. The fourth corner of the lever is formed to provide a follower'26 bearing at D against the cam 28 in segment 29 pivoted in the bracket and actuated by rotating shaft 32. The spring force tries to push lever 14 up at C which pushes down at A and up at B and-D. The lever is held against calibrating screw 24 and cam 28 by the spring.

When the shaft 32 is rotated, it rotates the cam 28 to raise or lower lever 14 at D. Since A and B are fixed, the lever 14 rocks about the axis determined by A-B to adjust C and the spring 10. If the calibrating screw 24 is adjusted, point B is raised or lowered and the lever 14 must rock about axis A-D to thereby adjust C and spring 10. Since the screw is supported by the bracket, any tool forces applied to the screw cannot influence the force of spring 10. Calibration of the spring is, therefore, isolated from undesired influences.

Segment 30 is provided with a serrated arc portion 34 against which lever 36 bears under influence of spring 38 coiled on a suitable support. Lever 36 acts to give positive feel to the adjustment and to hold the segment in its adjusted position. The left end of cam 28 is contoured at 40 to give a reset action to the plunger (not important here) and is shaped so the camwill not remain at the extreme position. To help the cam to rotate freely from this extreme position, the serrations are. not present at 42 so lever 36 can slide on the smooth surface at 42.

The cam is shaped so as it is rotated to have tab 26 act more towards the right portion of the cam, the tab can riseand relieve the pressure switch spring 10thus giving a low setting. At'44 the cam is cutout so the tab 26 can rise a substantial distance unless restrained. The restraint is provided by extra low calibrating screw 46 threaded through bracket 48 to limit rise of lever 14 by contacting tab E projecting therefrom. The screw 46 can be adjusted to calibrate the pressure switch for accurate response at extra low." This calibration is independent of the normal calibrationand vice versa. This arrangement permits very good response at extra low where tolerances in the calibration must, of necessity, be more rigid.

The segment is shaped at 50. to raise lever 36 to such extent that it strikes the switch plunger toactuate the switch for a light circuit advising the switch is set for .extra low."

The concept providing for accurate calibration at extra low" need not be used in conjunction with the wobble plate.

I claim: I

1. In a pressure switch of the type having a plunger arrangement for adjusting the effective spring force of the pressure switch and, hence, pressure to which it responds,

a bracket,

lever means mounted on the bracket and acting on the plunger to adjust the pressure switch,

actuating means acting on the lever means in opposition to the spring force of the pressure switch over a high-to-low range of settings and movable to an extra low" position in which it is ineffective .to limit the movement of the lever means in a direction reducing the force of the pressure switch spring,

positive limit means operative to engage and limit the lever means when the actuating means is ineffective,

said limit means including means for adjusting and calibrating the point of limitation whereby the pressure switch can be calibrated for extra low response.

' 2. Pressure switch according to claim 1 in which the adjusting means is a cam acting on the lever means and includes a portion allowing a substantial movement of the lever means at extra low" position subject to restraint by the calibrating means.

3. Pressure switch means according to claim 2 in which the cam is formed on a segment which rotates about an axis and the segment includes another portion, a second lever acting on said another portion frictionally engaged by said lever means,

. said another portion being shaped to actuate the second lever 

1. In a pressure switch of the type having a plunger arrangement for adjusting the effective spring force of the pressure switch and, hence, pressure to which it responds, a bracket, lever means mounted on the bracket and acting on the plunger to adjust the pressure switch, actuating means acting on the lever means in opposition to the spring force of the pressure switch over a high-to-low range of settings and movable to an ''''extra low'''' position in which it is ineffective to limit the movement of the lever means in a direction reducing the force of the pressure switch spring, positive limit means operative to engage and limit the lever means when the actuating means is ineffective, said limit means including means for adjusting and calibrating the point of limitation whereby the pressure switch can be calibrated for extra low response.
 2. Pressure switch according to claim 1 in which the adjusting means is a cam acting on the lever means and includes a portion allowing a substantial movement of the lever means at ''''extra low'''' position subject to restraint by the calibrating means.
 3. Pressure switch means according to claim 2 in which the cam is formed on a segment which rotates about an axis and the segment includes another portion, a second lever acting on said another portion frictionally engaged by said lever means, said another portion being shaped to actuate the second lever at said ''''extra low'''' position, and a switch actuated by said second lever at said ''''extra low'''' position.
 4. Pressure switch means according to claim 2 in which the calibrating means is a screw threaded through the bracket in position to contact the lever means at said ''''extra low'''' position to accurately calibrate the pressure switch at ''''extra low.''''
 5. Pressure switch means according to claim 4 including means to calibrate the position of the lever means over the high-to-low range without affecting the calibration at ''''extra low.'''' 